


Coffee, Or Something

by hyliank8



Category: Undertale (Video Game)
Genre: Dirty Talk, Fluff and Smut, Fucking at work, M/M, Sanster Week, Sanster Week 2021, SansterWeek2021, Sex is had, archive warning: skeleton porn, gaster and sans continue to be the horniest couple in the underground, i can think of literally nothing in this fic to add as a tag rn, i will add more tags in the morning when i have sobered up, kind of, obviously an important warning, ok going to bed now goodnight, this is not news to anybody, which comes as a surprise to no one
Language: English
Status: Completed
Published: 2021-03-02
Updated: 2021-03-02
Packaged: 2021-03-13 12:09:22
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 837
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29775963
Author URL: https://archiveofourown.org/users/hyliank8/pseuds/hyliank8
Summary: Sanster Week 2021 Day 2: Lab / Coffee  (prompt listhere on twitter, andhere on tumblr)Gaster has asked Sans to “bring a cup of coffee to his office.”  No other reason for calling Sans to his office.  Really.
Relationships: W. D. Gaster/Sans
Comments: 8
Kudos: 17





	Coffee, Or Something

**Author's Note:**

> oh god i almost rated this at a G instead of E lmfao whoops anyways ITS SANSTER WEEK and ok most of this was written sober but the ending half is not!! so!!! i will edit this sober tomorrow :)) and i mean actually edit it and not just leave it like the last three times
> 
> EDIT: I ALMOST FORGOT TO SAY this was inspired by a Very Good Gif my wonderful friend E88_02 made over on twitter 🙈 thank u friend ilu
> 
> for now,, enjoy!! and happy sanster weeeeek :DDDD

“h-hah, fuck...”

Sans whimpers, his arms shaking as he struggles to support himself on the desk as Gaster slowly thrusts deep inside of him. Sans’ soul hums pleasantly in his ribcage as the larger monster groans into the crook of his neck. There’s a warm, wet heat on his cervical vertebrae as Gaster bites and sucks at him fervently enough that Sans is certain he’ll have a mark to lie about to his co-workers later.

Sans had a feeling Gaster was hoping for a bit of something... _extra_ , when he paged Sans out of the blue to request that he bring a cup of coffee to his office. It’s been far too long since they’ve done this, their latest project eating up most of their waking hours in the past few weeks. Sans has missed his lover— _really_ missed him, and the way Gaster’s soul pulses with powerful affection for him reassures him that the feeling is mutual.

Sans is snapped out of his train of thought with a cry when Gaster’s cock presses up inside of him _just right_ the next time his hips rock forward. The arms supporting Sans’ own weight go limp for a minute as his mind is overrun with pleasure, but he manages to catch himself by jutting his elbows out behind him before he has the chance to fall entirely flat onto his back. Sans distantly notes the way the muted impact against the desk jostles the long-forgotten untouched cup of coffee on the desk beside them.

“You’re such a good boy, Sans...” Gaster murmurs. Every move the scientist makes is calculated, each word a specific effort towards ensuring that Sans will come utterly undone in his arms. “You’re being so good for me right now... do you love it? Do you love the way I fill you up like this?”

“y-yes, st- _stars,_ yes,” Sans manages through his heavy breaths. “i l-love you, gaster.”

“I love you, too,” Gaster replies, and Sans feels the larger monster’s powerful soul flutter as he says it. A moment later, his pace picks up. “Fuck... you feel so _good_ , Sans.”

The faster pace has Sans struggling to catch his breath. As Gaster grinds his hips against Sans’ clit with every thrust, the small skeleton can’t help the broken little sounds that fall from his mouth. The heat in his soul is building, becoming overwhelming—stars, he’s so, so close.

And judging from the way Gaster’s soul is tensing up, he’s not going to last much longer, either. His movements are becoming so powerful that the desk is jolting with the force of each thrust, and Sans revels in the way that it rocks his entire body back and forth. 

Sans has been in this position enough times to be able to tell when Gaster is starting to lose control, but he still has little warning before Gaster pushes him down against the desk. His huge hands pin him there as he angles his hips, pressing into him in a way that has Sans crying out all over again. Sans’ soul flutters as Gaster stares down at him through eyes half-lidded with lust, looking at him as though he’s the most beautiful thing in the world.

Sans notices distantly that they’ve knocked the full glass of coffee over, and that it’s spilled all over the floor, but he can’t bring himself to care and Gaster pays it no mind either. Stars, he’s so close.

All it takes is a few more thrusts before Gaster gives a guttural groan, his soul fluttering as he reaches his peak. He makes a clear effort to keep up his pace regardless, and it’s enough to send Sans over the edge a few moments later with a final cry of his lover’s name. Sans’ back arches as the waves of pleasure pound through his soul, and he feels the culmination of his being pulse in time with Gaster’s.

It takes a few moments for the waves of pleasure to finally recede. Gaster gives a relaxed sigh as he leans on the desk over Sans, placing a soft, sweet kiss on the top of his skull. Sans’ soul flutters at the gentle display of affection.

Stil buried deep inside of his lover, Gaster allows himself to rest on his arms braced on the desk on either side of Sans. Gaster’s body is so large that Sans is completely covered by him, his entire body enveloped in his lover’s shadow in the dim light of the room. They take a long moment to catch their breath before Sans breaches the comfortable silence.

“that... was amazing,” he murmurs, the cool aftermath of the pleasure still thrumming through his soul.

“Indeed,” Gaster agrees with a tame chuckle. “It’s been a while. I have... missed you.”

A radiant smile spreads across Sans’ face. “i’ve missed you too, wings.”

He pulls Gaster down into a kiss as they savor the afterglow together, letting their souls thrum in sync as they come down from their shared high.

**Author's Note:**

> Sanster Week 2021 prompt list [here on twitter](https://twitter.com/hyliank8/status/1365315685275074561?s=20), and [here on tumblr](https://hyliantimelordin221b.tumblr.com/post/644377725116858368/sanster-week-2021-is-here-starting-this) :)) 
> 
> u should participate!! it's been loads of fun so far :DD u can write or do art or whatever else u might wanna do (quint wrote a song!!!) there are two prompts for each day so u can choose which u one u wanna do, or u can try to do something with both if u would like to :D tomorrow's prompts are Dark / Sleeping At Work, and i already have a wartime sanster ficlet in the works for that one but i also have a very busy day tomorrow so who knows whether i'll post it in time :'D ANYWAYS
> 
> here's my [tumblr](https://hyliantimelordin221b.tumblr.com/) and [twitter](https://twitter.com/K8Maybe), i like to talk about sanster a little bit sometimes 🙈 come join meeee!!
> 
> if u comment i lov u


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